Hardening metal articles by nitrogenization



Patented Dec. 3, 1929 STATES PATENT; OFFICE ADOLF FRY, OF IlSSEN, GERMANY, ASSIGNOR, .BY MESNE ASSIGNMENTS, TO THE NITRALLOY CORPORATION, A. CORPORATION 011 DELAWARE HABDENING METAL ARTICLES BY NITROGENIZATION No Drawing. Application filed October 31, 1928, Serial No. 316,362, and in Germany Novembenfl, 1927.

The invention relates to a method for protecting certain portions of a metal article to be hardened by nitrogenization from acquir ing the nitrogenization hardness. This method may be performed e. g. in the following manner: I

The metal articles to be hardened bynitrogenization are provided on the portions that are to be protected from acquiring the nitrogenization hardness with a coating ofv a salt, a salt mixture or of a glazingor enamel-like mass that during the hardening treatment protects the covered places from the action and penetration of nitrogen. It has been proved to be particularly suitable to provide the places to be protected with a coating of potassium chloride or with a'mixture of 2.0

. parts by weight of barium chloride, 1.5 parts by weight of potassium chloride, 1.0 part by weight of calcium chloride, and 1.25 parts by weight of sodium chloride or with a mixture of 7 parts by weight of lead oxide, 2 parts by weight of sand, and 1 part by weight of borax. In applying such a coating, one may advantageously proceed as follows:

The places to be protected are painted with water glass and immediately thereafter coated, for example, with pulverizedpotassium chloride. If required this treatment is performed several times.

In the same manner one proceeds in applying a salt mixture impermeable to nitrogen. The above-indicated mixture of lead oxide, sand, and borax is first melted, granulated and finely ground and is then applied in the manner described for the pulverized potas-' sium chloride. I

After the work piece has been treated in the indicated manner, it is subjected to the proper nitrogenization hardening operation in which its unprotected portions are nitrogenized by a known process, for example, that disclosed in my U. S. Patent No. 1,487,554, whilst the portions previously coated as described with the protective means remain so soft that they can be machined without any difficulty.

The expression alkaline chloride as used in the appended claims is to be understood as including the chlorides of the alkali metals selected portions of a metal article, the steps which comprise applying onthe portions tobe protected a coating consisting of an alkaline chloride composition including potassium chloride and infusible at a nitrogenizing temperature and thereafter subjecting said article to a nitrogenizing treatment.

3. In the hardening by nitrogenization of selected portions'of a metal article, the steps whichcomprise applying on the portions to be protected a coating consisting of a mixture of alkali and alkaline earth metal chlorides, said mixture being substantially infusible at a nitrogenizing temperature, and

thereafter subjecting said article to a nitrogenizing treatment.

4. In the hardening by nitrogenization of selected portions of a metal article, the steps which comprise applying on the portions to be protected a coating consisting of a mixture of the following alkaline chloridesin about the proportions stated by weight: 2.0 parts barium chloride, 1.5 parts potassium chloride, 1.0 part calcium chloride, 1.25 parts sodium chloride, and thereafter subjecting said article to a nitrogenizing treatment.

'5. In the hardening by nitrogenization of selected portions of a metal article, the steps which comprise applying on the portions to be protected a coating of sodium silicate, then applying to the thus coated portions a coating consisting of an alkaline chloride composition substantially in-fusible. at a nitrogenizing temperature, and thernafter subjecting said article to a nitr'ogenizing treatment.

6. In the hardening by nitrogenization of selected portions of a metal article, the steps 7 which comprise applyingon the portions to be protected 9. coatin of sodium silicate, then applying to the t us coated portions a coating consisting of an alkaline chloride "composition including potassium chloride and I infusible at a nitrogenizing temperature, and thereafter subjecting said article to a nitrogenizing treatment.

7. In the hardening by nitrogenization of selected portions of a metal article, thetsteps which comprise applying on the portions to be protected a coating of sodium silicate, then applying to the thus coated portions a coating consisting of a mixture of alkali and alkaline earth metal chlorides, said mixture being substantially 'infusible at a nitrogenizing temperature, and thereafter subjecting said article to anitrogenizing treatment.

8. In the hardening by nitrogenization of selected portions of a metal article, the steps which comprise applying on the portions to be protected acoating of sodium silicate, then applying to the thus coated portions a coating consisting of a mixture of the following alkaline chlorides in about the proportion stated by weight 2.0 parts barium chloride, 1.5 parts potassium chloride, 1.0 part calcium chloride,

1.25 parts sodium chloride, and thereaftersubjecting said article to a nitrogenizing treatment.

9. A nitrogen-impenetrable coating com position consisting of a mixture of the following alkaline chlorides in about the roportions stated by weight: 2.0 parts barlum chloride, 1.5'parts potassium chloride, 1.0 part calcium chloride, 1.25 parts sodium chloride.

The foregoing specification signed at Cologne, Germany, this'6 day of October,

ADOLF FRY; 

